Abstract A system and probe for indicating the level of material in a vessel as a function of material capacitance comprising a resonant circuit including a capacitance probe adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level. An rf oscillator has an output coupled to the resonant circuit and to a phase detector for detecting variations in phase angle as a function of probe capacitance. Level detection circuitry is responsive to an output of the phase detector and to a reference signal indicative of a predetermined level of material for indicating material level as a function of a difference between capacitance at the probe and the reference signal. In the preferred embodiments of the invention disclosed, an automatic calibration circuit adjusts the resonance characteristics of the parallel resonant circuit of the reference signal indicative of a predetermined reference material level.
A system for indicating the condition of material in a vessel as a function of material capacitance comprising a capacitance probe adapted to be disposed in said vessel so as to be responsive to variations in capacitance as a function of material condition in said vessel, oscillator means for providing a periodic electrical signal, circuit means for coupling said periodic electrical signal to said capacitance probe, means for generating a reference signal for calibration purposes, detection means responsive the capacitance at said probe and said reference signal for indicating the condition of material in a vessel, calibration means for automatically varying the reference signal, and means responsive to said detection means and to said calibration means for automatically terminating said varying of said reference signal when said detection means detects a predetermined relationship between said probe capacitance and said reference signal whereupon the system is calibrated for proper indication of the material condition.
Claim 2
Independent Claim
153 words
A system for indicating the condition of material in a vessel as a function of material capacitance comprising a capacitance probe adapted to be disposed in said vessel so as to be responsive to variations in capacitance as a function of material condition in said vessel, oscillator means for providing a periodic electrical signal, circuit means for coupling said periodic electrical signal to said capacitance probe, means for generating a reference signal for calibration purposes, detection means responsive the capacitance at said probe and said reference signal for indicating the condition of material in a vessel, calibration means for automatically varying the reference signal, and means responsive to said detection means and to said calibration means for automatically terminating said varying of said reference signal when said detection means detects a predetermined relationship between said probe capacitance and said reference signal whereupon the system is calibrated for proper indication of the material condition.
Claim 3
Dependent Claim
35 words
The system of claim 1 wherein said means for generating a reference signal comprises a plurality of capacitors and a corresponding plurality of electronic switch means for selectively connecting said capacitors to said probe capacitance.
Claim 4
Independent Claim
51 words
The system of claim I wherein said calibrating means comprises counter-means having outputs operatively connected selectively to control conductive conditions at said switch means, and means responsive to said initiating means and to said means for terminating said calibration for automatically varying the count in said counter-means during the calibration operation.